Vacuum Audio
Calculators
Est. in the age of the thermionic valve

Vacuum Audio
Calculators

A workbench of 24 interactive calculators for designing, modding and servicing valve amplifiers: from triode load lines and tone stacks to rectifiers, bias and output transformers. Every page draws its own schematic or curve and explains the engineering behind it.

Start with a load lineTwist a tone stack

Gain Stages

Triodes, load lines, bias and the small-signal world.

Ia
Triode Load Line
Plot plate curves, find the operating point, gain and headroom.
→µ
Gain Stage Response
Full frequency response of a common-cathode stage.
→Rk
Cathode Bias & Bypass
Size Rk, its wattage and the bypass capacitor shelf.
→CF
Cathode Follower
Gain, output and bootstrapped input impedance.
→±
Long-Tailed Pair
Phase inverter gains and plate-load balancing.
→Cm
Miller & Grid Stopper
Input capacitance and high-frequency roll-off.
→

Output Stage

Power valves, transformers, feedback and loudness.

W
Output Power Estimator
Max clean watts from B+, load and topology.
→N²
Output Transformer Match
Turns ratio and reflected impedance for any tap.
→mA
Power Valve Bias
Idle dissipation, % of rating and target current.
→Lp
Transformer Bandwidth
Primary & leakage inductance frequency limits.
→β
Feedback & Damping
Global NFB, output impedance and damping factor.
→dB
Power & Loudness
SPL from watts, sensitivity and distance.
→

Power Supply

Rectifiers, filters, heaters and safety.

⏦
Rectifier & Ripple
B+ voltage, ripple and reservoir sizing.
→LC
RC / LC Filter
Ripple attenuation, voltage drop, resonance.
→B+
B+ Dropping Chain
Node voltages through a decoupling chain.
→6.3
Heater Current
Winding currents and DC heater resistor.
→⚡
Bleeder Resistor
Discharge time to a safe voltage.
→

Tone & Signal

Tone stacks, coupling and passive networks.

TMB
FMV Tone Stack
Fender / Marshall / Bassman frequency response.
→Cc
Coupling Capacitor
High-pass corner and cascaded phase shift.
→Cb
Bright Cap & Volume
Treble lift of a bright cap vs. volume setting.
→X
Reactance & Resonance
Xc, XL, LC resonance and RC time constant.
→

Bench Utilities

Everyday conversions for the workbench.

dBV
dB & Level Converter
dBV, dBu, dBm and gain ratios.
→Ω
Ohm's Law & Power
V, I, R, P and resistor wattage.
→∥
Series / Parallel
Combine resistors or capacitors, hit a target.
→
⚠

Danger: High Voltage

Valve amplifiers operate at several hundred volts and their capacitors can hold a lethal charge long after switch-off. These calculators are design aids based on simplified models; always verify with measurements, discharge capacitors, and work with one hand behind your back.